I am learning akka stream and encounter Keep.left and Keep.right in the code:
implicit val system = ActorSystem("KafkaProducer")
implicit val materializer = ActorMaterializer()
val source = Source(List("a", "b", "c"))
val sink = Sink.fold[String, String]("")(_ + _)
val runnable: RunnableGraph[Future[String]] = source.toMat(sink)(Keep.right)
val result: Future[String] = runnable.run()
What does here Keep.right mean?
Every stream processing stage can produce a materialized value which can be captured using viaMat
or toMat
(as opposed to via()
or to()
, respectively). In your code snippet, the using of source.toMat(sink)
indicates that you're interested in capturing the materialized value of the source and sink and Keep.right
keeps the right side (i.e. sink) of the materialized value. Keep.left
would keep the materialized value on the left side (i.e. source), and Keep.both
would allow you to keep both.
More details is available in relevant sections in the Akka Streams documentation.
Keep.left
keeps only the left (first) of the input values. Keep.right
only keeps the right (second) of two input values.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With